Howdy everyone,

It's been awhile since I've posted on here! Lately my truck ('77 2wd F150 SuperCab Trailer Special) has developed some kind of pulsating vibration. It's not major by any means, but it's kind of one of those annoying things. It's felt only in the floor and seat. It doesn't vibrate the wheel, dash, rearview or side view mirrors. It happens at pretty much any speed above 50mph. It really doesn't matter if its hot or cold either. It only does it when in gear and holding a constant speed or accelerating. If I let off the gas or shift into neutral, it diminishes some but doesn't completely go away.

Here's what the work that's been done recently that hasn't really phased it much at all:

- The engine was rebuilt. Mostly stock 460 with some bolt on goodies. Runs amazing! It's externally balanced and DOES have the correct weighted crank spacer and weighted flywheel (it's new also). Vibration has been present both before and after the rebuild.

- Stock fan, new fan clutch, new power steering pump, new water pump and new 150A alternator installed. Higly doubt they affect the vibration, but have run the truck with the belts off in the driveway and everything feels the same.

- New exhaust system. Dual 2.5" pipes heading into a "dual in single out" muffler. Tailpipe is mounted in the stock location behind the axle. Vibration was present before and after the exhaust rebuild.

- Newer tires that were mounted and balanced by me. Standard issue 235/70r15 Dextero DHT2 tires. They're a tad small but get the job done and look okay for now. I plan on rebalancing them this spring like I always do, but this definitely does not feel like a tire vibration.

- All brakes have been rebuilt. New wheel bearings up front when I did the brakes. Currently no noise or play in them. Plan on re-greasing them this spring like I usually do but I have my doubts they're an issue.

- New center driveshaft (2pc shaft) and rebalanced rear shaft. Original center shaft had two dents in it. New center support bearing and Neapco U-joints. Vibration was present before and after the driveshaft work.

- Radius arm bushing were replaced by the previous owner. King pins are original and are not stuck. Tie rods were replaced by me. Everything is kept very well greased.

- Body mount bushings are original, but all appear to be intact.

- Engine and transmission mounts are all new as well. Anchor brand mounts. All went in fine and are not "loaded" or "tweaked" in any way to be grounding out against the frame intermittently.

I think that about sums it up. It's not a ground pounding heart stopping vibration. It's just a rolling, rhythmic, churning feeling vibration that you feel in the seat. You don't even feel it in the pedals! I plan to check the pinion angles just to make sure they're on, but outside of that I'm out of ideas. The transmission (C6) has never been rebuilt but has had the fluid changed and still runs Type F fluid. The rear end (Ford 9" with 3.23:1 gears) has also never been apart fully, but has had the fluid changed out to 80wt90.

To put it all in one place, my truck is a '77 F150 Supercab with a '79 460 mated to the stock C6 and stock 9" rear end.

 

Check rear wheel bearings.

 

Part of me was assuming they'd make noise when they go bad, but part of me also wonders if they could be the culprit. It's certainly worth a look.

 

High frequency vibrations are pre final ratio.

Low frequency vibrations are post final ratio.

pulsating sounds low to me so if you confirm then you should check things like:

wheel yaw
tire condition
wheel bearings
rotor runout
brake caliper condition

 

Wheel yaw I will have to check into. I have never had the truck aligned at all but it goes down the road straight and the front tires are worn correctly.

The tires are in good shape all the way around. No shifted belts, and each wheel/tire has no more than 3-4oz of weight on them. The rear tires are from 2015 and still have about 6-7/32" of tread left, and the front tires are from 2018 and have 8/32" left on them. They are not in any way shape or form aggressive knobby tires. They are average all weather Light truck/SUV tires.

Front bearings are good. As I said I'm planning on repacking them early this spring like I do at the start of every year. The rears to my knowledge have never been changed or touched.

Rotor runout is comething that can be checked, but they do not feel as if they are warped at all when I step on the brakes. They are also fairly new (about 3yrs old with about 20,000 miles on them)

Brake calipers are also fairly new as well because they were replaced when I did the front brakes 3 years ago. They don't seem to be hanging up, as my pads have equal wear side to side.

At this point I'm wondering if it could be the torque converter or something in the trans as well. It has always dripped a little ATF out the bellhousing inspection cover, but it's never enough to leave a puddle on the ground. I'm sure that's just the front pump seal, but I was planning to replace that whenever I rebuild the trans.

 

Look at the transmission dipstick (or owner's or shop manual) and see which fluid type is specified for 1977. I could be wrong, but somehow I thought that they stopped using type F somewhere in 1976.

 

sounds like early bearing failure. i have had new bearings not last 3 years (i bought from the locale parts store), same symptoms as you are describing. went with timken bearings from jbg this time, so far so good.

 

The first thing you need to do is identify if high frequency or low frequency.

That will tell you what components to look at.

Was the same pulsating present before the current set of tires?

 

The vibration started roughly in the middle of last summer. It's been pretty consistent since then. I've cross switched the tires front to back and left to right, then diagonally, etc. That didn't change anything.

The pulsing comes in above 55mph. I cannot drive out of it. It is not proportional to the engine rpm at all and doesn't really increase a whole lot with speed.

 

Not to go off topic, but I like the 442 in the background of your pic.

I have a vibration similar to what you're experiencing, but I haven't really looked into it much yet. I'll be interested to see what it is if you nail it down to something.

 

Have you checked the bearings in the rear diff? Pinion bearings and side bearings.

 

The rear end is original minus the fluid. It's never given any indication of being worn out, but anything is suspect at this point.

 

A relatively easy and cheap check would be u-joints.

Just a thought.

 

The u joints and shafts have been very well checked. Please see my first post.

 

Sorry, missed that.